sifive: reset: add DM based reset driver for SiFive SoC's

PRCI module within SiFive SoC's has register with which we can
reset the sub-systems within the SoC. The resets to DDR and ethernet
sub systems within FU540-C000 SoC are active low, and are hold low
by default on power-up. Currently these are directly asserted within
prci driver via register read/write.
With the DM based reset driver support here, we bind the reset
driver with clock (prci) driver and assert the reset signals of
both sub-system's appropriately.

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@sifive.com>
Reviewed-by: Pragnesh Patel <Pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Bin Meng <bin.meng@windriver.com>

arch/riscv/include/asm/arch-fu540/reset.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2020 SiFive, Inc.
+ *
+ * Author: Sagar Kadam <sagar.kadam@sifive.com>
+ */
+
+#ifndef __RESET_SIFIVE_H
+#define __RESET_SIFIVE_H
+
+int sifive_reset_bind(struct udevice *dev, ulong count);
+
+#endif